Ferrule with relief to reduce galling

ABSTRACT

High localized loading, galling, and high torque forces have been generally eliminated or greatly reduced in a two ferrule tube fitting assembly through suitable modification of the rear ferrule so as to redirect the reaction forces acting between the front ferrule and the drive nut. The rear ferrule has a cylindrical interior wall that closely surrounds the tube end and is provided on the interior cylindrical wall with a circumferentially continuous radial recess that is located between the nose and rear wall of the rear ferrule. The rear ferrule also has a radially external wall that is substantially conical and additionally shaped to extend radially outward toward the enlarged diameter portion or flange of the rear ferrule. The rear ferrule further includes a contoured face on the rear driven surface of the ferrule that engages the drive surface of the drive nut.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/054,186 filed on Apr. 2, 1998 now U.S. Pat. No. 6,131,963,which is a continuation-in-part of U.S. patent application Ser. No.08/834,255 filed on Apr. 15, 1997, now U.S. Pat. No. 5,882,050, theentire disclosures of which are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

The subject invention is directed to the art of ferrule type tubefittings. More particularly, the invention concerns a two ferrulefitting wherein the rear ferrule is designed to reduce the torquerequired to rotate the associated nut and to also reduce galling betweenthe rear ferrule and the interior surface of the drive nut. Theinvention may also be applied in a single ferrule fitting.

A commercially available and highly successful two ferrule fitting usedfor tubing is illustrated in FIGS. 1 and 1A. FIG. 1 shows the fittingcomponents in a finger tight position preparatory to final tightening,whereas FIG. 1A shows the fitting after final tightening. As shown, thefitting comprises a body 10 having a cylindrical opening 12 counterboredfor receiving tube end 13. A tapered, frusto-conical camming mouth 14 islocated at the axial outer end of the counterbore. A front ferrule 16having a smooth, cylindrical inner wall 18 is closely received on thetube. The front ferrule has a frusto-conical outer surface 20 to bereceived in the camming mouth.

Associated with the front ferrule 16 and located axially outwardtherefrom is a rear ferrule 22 configured as shown with a tapered noseportion 24 and a rear flange 26 having an inclined end surface 28. Theinclined end surface of the rear ferrule 22 provides a radial componentas well as an axial component of the pull-up forces acting on the endsurface as will be apparent to those skilled in the art. The taperednose 24 enters a tapered camming surface in the rear surface of thefront ferrule.

The ferrules 16, 22 are enclosed by a drive nut member 30 threaded tothe body 10. During tightening and make-up of the fitting, the inner endface, flange, or shoulder 32 of the nut acts against the rear wall endsurface 28 of the rear ferrule to drive the ferrules forwardly into thefully engaged position shown in FIG. 1A.

The small diameter portion or nose of the rear ferrule is dimensioned sothat it plastically deforms during make-up of the fitting. This actionis desirable since it results in tight gripping engagement of the outerwall of the tubing. The thickness of the nose portion cannot be reducedto an extent that the rear ferrule deforms too much and only the rearferrule adequately grips the outer wall of the tubing. That is, the twoferrule assembly requires desired deformation of both the front and rearferrules for the gripping and sealing capabilities that have made thistwo ferrule assembly a commercially successful product. On the otherhand, the thickness of the nose of the rear ferrule cannot be enlargedto such an extent that it results in a structural arrangement that istoo stiff and does not permit the desired rear ferrule deformation.

A more complete description and understanding of the conventional twoferrule phase controlled sequential gripping action resulting from theinclined rear surface and the interaction of the front and rear ferrulesis set forth in U.S. Pat. No. 3,103,373 issued to Lennon, et al., theentire disclosure of which is fully incorporated herein by reference.

Accordingly, it will be recognized by those skilled in the art that apredetermined wall thickness of the nose of the rear ferrule is desiredthat achieves the desired gripping of the tube and cooperates with thefront ferrule in such a manner that it achieves its desired goals ofgripping and sealing the tube.

It is also recognized that operators of fluid systems test the systemprior to a production run by pressurizing the system to an appropriatefactor times the rated system pressure. In this manner, the operator caneasily detect whether the fluid system is sealed, i.e. that there are noleaks. With this knowledge, the manufacturer can provide a fitting inwhich the nose of the rear ferrule will not have any additional plasticdeformation at the elevated test pressure. Accordingly, the elevatedtest pressure is used to determine the desired wall thickness of thenose portion of the rear ferrule to achieve the desired amount ofdeformation of the nose and permit the front and rear ferrules toproperly grip and seal with the outer wall of the tube.

It has also been found that galling of the drive nut sometimes occurs inthe drive face area of engagement between the inner end face of thedrive nut and the rear wall of the rear ferrule. After analysis, it isbelieved that the axial thrust or pull-up force between the front andrear ferrule is essentially parallel to the axis of the fitting. Thisaxial thrust causes the rear comer region of the rear ferrule toselectively concentrate pull-up stress at the inside drive surface ofthe nut particularly in a localized area to produce the galling. Thisalso noticeably increases the nut torque forces experienced duringmake-up even if galling is absent. Accordingly, it would be highlydesirable to provide a design wherein the thrust forces do not producethe high localized loading with the resultant galling and high torqueforces.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a tube fittingincludes a fitting body having a cylindrical bore for receiving a tubeend and including a tapered mouth at one end of the bore; a drive memberhaving a threaded engagement with the body and having a ferrule drivesurface; a first ferrule having a tapered first end that extends intothe tapered mouth of the fitting body and having a second end with atapered recess that axially extends toward the first end; and a secondferrule having a cylindrical interior wall, a tapered first end thatextends into the tapered recess of the first ferrule, and having acontoured face on a second end thereof that engages the drive memberferrule drive surface; the second ferrule interior wall having acircumferential recess located between the first and second ends of thesecond ferrule; the recess and the contoured face reducing stressconcentrations on the drive member drive surface when the fitting ismade up.

Another aspect of the invention includes forming the rear ferrule with acylindrical interior wall that has a first diameter at the forward ornose end of the ferrule and a second diameter at the rear end of theferrule wherein the second diameter is greater than the first diameterso that, for example, a single tool can be use to form thecircumferential recess and the cylindrical wall. Still a further aspectof the invention includes forming a notch on the outside diameter of theferrule body that joins the second ferrule first and second ends. Inanother aspect of the invention, a contoured drive surface is providedon the drive member rather than on the rear ferrule second end. Thepresent invention may also be practiced with ferrules that are made ofharder base metal than prior ferrules. The invention may also bepracticed with ferrules that have been case hardened either entirely orselectively on the ferrule surface. In general, the present inventionmay be used in single ferrule fittings as well.

These and other aspects and advantages of the present invention will beapparent to those skilled in the art from the following description ofthe preferred embodiments in view of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, preferred embodiments and a method of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

FIG. 1 is a longitudinal cross-sectional view of a well known prior arttwo ferrule swage-type fitting;

FIG. 1A is an enlarged view of the circled area of FIG. 1 showing theprior art fitting in a made-up condition;

FIG. 2 is a view like FIG. 1 but showing a preferred embodiment of afitting incorporating a modified rear ferrule designed to improvereaction force transmission through the rear ferrule;

FIG. 3 is a greatly enlarged showing of the circled area of FIG. 2;

FIG. 4 is a detailed, partial cross-sectional view of a preferred formof rear ferrule;

FIG. 5 is a cross-sectional view similar to FIG. 4 showing a secondpreferred form for the rear ferrule;

FIG. 6 is a cross-sectional view of the fitting of FIG. 1 particularlyshowing the rear ferrule positioned between the front ferrule and thenut at initial make-up (graphically meshed for finite element analysis);

FIG. 7 is a view of the fitting of FIG. 6 in a made-up condition andillustrating the stress concentrations;

FIG. 8 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

FIG. 9 is a view of the fitting of FIG. 8 in a made-up condition andillustrating the stress concentrations;

FIG. 10 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

FIG. 11 is a view of the fitting of FIG. 10 in a made-up condition andillustrating the stress concentrations;

FIG. 12 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

FIG. 13 is a view of the fitting of FIG. 12 in a made-up condition andillustrating the stress concentrations;

FIG. 14 is a table of different geometrical variations of the rearferrule configuration;

FIG. 15 is a cross-sectional view of an alternative embodiment of a twoferrule fitting;

FIG. 16 is an enlarged view of the ferrule region of the embodiment ofFIG. 15;

FIG. 17 is a partial view of a rear ferrule with a contoured face inaccordance with one aspect of the invention;

FIG. 18 is a partial view of a contoured rear ferrule shown in theengaged position with a front ferrule and drive nut surfaces prior topull up;

FIG. 19 is a view of the embodiment of FIG. 18 in the pulled upcondition showing stress distributions;

FIG. 20 is another embodiment of the invention;

FIG. 21 illustrates stress distributions in a two ferrule fitting thatdoes not use a contoured rear ferrule;

FIG. 22 illustrates another embodiment of a rear ferrule designincorporating a circumferential recess;

FIGS. 23A-F illustrate various alternative rear ferrule driven surfaceprofiles;

FIGS. 24A-G illustrates an alternative embodiment of the inventionwherein the drive surface of the nut is provided with a contour surface;

FIG. 25 illustrates another alternative embodiment of a ferrule havingan inner cylindrical bore formed of two different diameters;

FIG. 26 illustrates another alternative embodiment of a ferrule havingan outer notch or recess in the ferrule body;

FIG. 27 illustrates another alternative embodiment of the invention of aferrule having a notched inner bore, a contoured rear surface, an outernotch and a crown portion on the ferrule nose region; and

FIG. 28 is a finite element analysis illustrating one aspect of theinvention of a high friction tube grip area axially spaced from a stressriser created at the nose of the ferrule.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposesof illustrating preferred embodiments of the invention only and not forpurposes of limiting same, FIGS. 2-4 illustrate the overall arrangementof a fitting incorporating the invention. It should be noted that inmany of the illustrations herein of the ferrule profiles, the ferrulesare shown in partial cross-section for clarity and ease ofunderstanding, particularly for views of the ferrule geometry andprofile wherein it is only necessary to illustrate a portion of theentire ferrule in sectional view. The FIGS. 2-4 embodiment has the majorcomponents identified with the same reference numerals used with respectto the description of the prior art device of FIGS. 1 and 1A. Adescription of a FIG. 1 element is to be taken as equally applicable tothe FIGS. 2-4 elements that are correspondingly numbered unlessotherwise noted. In particular, in the FIGS. 2-4 embodiment, the rearferrule 22′ has been modified in a manner to cause the reaction forcesacting between the front ferrule through the rear ferrule to the nut tohave a significant force component that is directed radially outward.This is in contradistinction to the FIGS. 1 and 1A embodiment whereinthe force component under consideration has a high axial component.Specifically, as shown in FIG. 4, force component A extends generallyaxially of the rear ferrule 22′ and results in an increase in the loadsapplied at the radial inner face of the ferrule surface 28′ and theflange 32′ of the nut. As previously discussed, high localized loadingor stress concentration in this area produces high torque and galling.

While the invention is described herein with particular reference to atwo ferrule system, such explanation is exemplary in nature and shouldnot be construed in a limiting sense. Various aspects of the presentinvention may also find application in a single ferrule fitting.

In one embodiment of the invention, a redirection of the reaction forcesis achieved by providing a circumferential recess 40 throughout theinner surface of the ferrule 22′. Note that a recess 40 is locatedgenerally midway between the opposite ends of the ferrule 22′ and thisresults in the inner surface of the rear ferrule being reduced to tworelatively axially narrow substantially cylindrical and continuouscontact areas 42 and 44. By so modifying the rear ferrule, the forceswhich are conducted from the front ferrule through the rear ferrule tothe nut surface or flange 32′ tend to be directed more radially outwardsuch as diagrammatically illustrated by the force line B of FIG. 4. Inthis embodiment, the generally flat contact areas 42 and 44 havesubstantially the same diameter; however in an alternative embodiment,these two regions may have different diameters, for example it may bedesirable in some applications to have the diameter of the rear flatarea 42 slightly greater than the diameter of the forward flat area 44,for example, by a few thousandths, more preferably one to threethousandths of an inch. In yet a further alternative embodiment, therear flat area 42 may be eliminated as a contact area by providing acounterbore in this area. Particularly for larger ferrule sizes, thesingle flat in the nose section of the rear ferrule may be sufficient tomaintain proper ferrule alignment on the tubing during installation.These alternatives will be more fully described hereinafter.

Another important feature of the invention is best exemplified bycomparing the rear ferrule 22 of FIG. 1 with the rear ferrule 22′ of theFIGS. 2-4 embodiment. Particularly, the outer radial wall 50 of the rearferrule 22′ includes a conical section that increases in radialdimension as it extends from the forward nose portion 52, that isreceived in the rear chamfer region 53 of the front ferrule, to the rearflange 26′. In the prior art arrangement (FIGS. 1 and 1A), the rearferrule has a cylindrical through bore and an outer radial wall thatextends parallel to the inner surface defining the through bore in thisregion. In other words, the rear ferrule has a constant annular wallthickness “t”. In the embodiment of FIGS. 2-4, the outer wall has theconical or tapered configuration that provides sufficient wall thickness“t” and controlled deformation of the nose portion when the recess isincorporated into the modified rear ferrule. Preferably, the outer wall50 has a generally uniform angle or taper as it extends between thereduced dimension nose region 52 received in the camming mouth of thefront ferrule and the enlarged diameter rear flange 26′. Again, thisprovides controlled deformation of the rear ferrule so that the region52 is plastically deformed radially inward along surface 44 intogripping, sealed engagement with the outer wall of the tube. Note thatin FIG. 4 the recess 40 is so shaped as to appear that the dimension “t”is constant, though it need not be. For example, if the recess 40 isformed such as in many of the illustrations of FIGS. 14, 17 and 18, thetapered outer wall 50 provides a non-uniform thickness “t” between therear ferrule nose 52 and the rear flange 26′.

The wall thickness “t” and the geometry and configuration of the rearferrule 22′ are selected for a particular application in order tobalance and properly align the ferrule 22′ on the tubing and to assurethat the rear ferrule 22′ cooperates with the front ferrule 16′ toachieve the desired phase controlled sequential gripping operationduring pull-up to assure a proper seal on the tubing. During fittingpull-up, the rear ferrule 22′ applies a vector force against the outersurface of the tube end 13 that has both axial and radial components.The radial component force enables an axial friction force on the tubesurface to achieve excellent gripping and sealing action. This axialfriction force balances against an axial tube grip reaction force fromthe tube 13.

The combined geometry of the tapered outer wall 50 along with the recess40 cause a “hinge” effect of the rear ferrule nose portion 52. Theselected geometry and configurations will depend on such factorsincluding but not necessarily limited to the materials used for thefitting components, the tube material and wall thickness, the operatingpressure for the fitting, whether the rear ferrule is to be casehardened or not, and so forth. In order to maintain proper sequentialgripping operation during make-up, it is important that the rear ferrule22′ nose portion 52 does not collapse too soon otherwise the frontferrule 16 may not have sufficient gripping force on the tube wall or aninadequate seal force between the front ferrule 16 and the taperedcamming mouth 14. If the rear ferrule 22′ collapses too late relative tothe front ferrule, then the rear ferrule 22′ may not have adequategripping force on the tube 13 wall.

The rear ferrule 22′ hinge effect directs the rear ferrule applied forceat the nose section 52 against the tube wall at a significant radialvector angle from the tube surface. This ferrule applied force vector Bthus has a significant radial component while enabling the significantaxial friction force. Thus, a smaller axial component force applied viathe drive member 30 sufficiently opposes the axial tube grippingreaction force in contrast to when the applied force is substantiallyaxial as in the prior art of FIGS. 1 and 1A. The rear ferrule 22′ gripof the tube 13 thus approaches a toggle-like hinged action. The smalleraxial component force results in reduced nut 30 pull-up torque toachieve the same tube grip.

In addition, during fitting pull-up, this hinge characteristic directsthe tube reaction force through the rear ferrule 22′ generally towardthe central region of the rear ferrule driven surface 28′ that contactsthe drive surface of the nut shoulder 32′. This results in the reactionforces being more evenly distributed across the rear ferrule 22′ drivensurface 28′ to avoid or reduce high concentrations of stress, thusreducing or eliminating galling and reducing pull-up torque without lossof tube gripping force. In many cases it may be preferred that thereaction forces be directed in a direction generally normal to the rearsurface 28′ of the rear ferrule. The increased tube gripping forceresulting from the applied radial force also imparts greater penetrationor swaging of the rear ferrule 22′ nose portion onto the tube 13. Thisprovides an excellent tube grip and seal with lower applied torque, andalso provides greater resistance to vibration fatigue by providing aswaged region of high gripping pressure behind (i.e. axially rearward)of the tube stress riser created at the forward end of the nose of therear ferrule 22′. FIG. 28 illustrates this result, in that the stressriser region 400 where the nose penetrates the tube wall 13 is axiallyforward of a swaged region 402 of high frictional engagement between theferrule nose and the tube wall. High frictional area or swage produces acollet effect that secures the ferrule on the tube wall and protects thestress riser 400 from vibration. Good gripping action of the rearferrule forward flat section 44 of the nose portion onto the tube isimportant for overall performance of the fitting, in contrast to anycontact pressure between the rear ferrule rear flat portion 42. In manycases, there is no need for an contact between the portion 42 and thetube 13.

Another benefit resulting from the reduced galling and lower pull-uptorque of the present invention is that re-make of the fitting isfacilitated. By “re-make” is simply meant that, in some applications,the user desires to separate a tube fitting after installation, possiblyto replace a valve, tubing or to perform other routine maintenance andrepair, and then to re-install the same fitting without replacing theferrules and/or nut or body. If the rear ferrule and drive nut havebecome galled, then the torque required for re-make of the fitting maybe prohibitive or impossible, or the fitting may not adequately re-seal.With the use of the present invention to significantly reduce oreliminate galling and reduce pull-up torque, re-make is facilitated.

Although the present invention is useful with many different materials,it has particular advantages when used with stainless steel fittings andtubing, including but not limited to 316 and 316L stainless tubing, butincludes in addition to other alloys, Hastalloy, Inconel, Monel alloys400 and 500, 254SMO and steel, and duplex stainless steel such as, forexample, SAF 2507. The present invention can be used with or withoutcase hardening on all or part of the surfaces of the ferrules asrequired.

With respect to case hardened ferrules or ferrules made of materialssubstantially harder than 316L stainless steel, the present inventionallows the fitting 10 to be properly pulled up with the desired phasecontrolled sequential gripping of the tube wall. If a conventionalferrule, particularly the rear ferrule, was case hardened or made of avery hard material, the ferrule would be too stiff to achieve properseal and grip of the tube wall. The present invention howeverfacilitates the use of ferrules of hard materials or that have been casehardened over part or all of their surface. Case hardening herein refersto the treatment of the ferrules in such a manner as to provide a carbonor nitrogen rich surface that substantially hardens the ferrule body ascompared to the underlying base metal, as is known to those skilled inthe art.

FIG. 5 illustrates another preferred embodiment of the rear ferrule inwhich the recess 40 has is defined by two different angles (an obtusetriangle). For example, the smaller first angle defined with the innersurface increases as it extends rearwardly from the surface 44 towardthe rear flange 26′. The larger second angle (approximately twice theangular dimension of the first angle) increases as it extends forwardlyfrom the surface 42 toward the nose region. These angles thus intersectat an axial position that is located beneath the intersection of theouter wall 50 with the rear flange. Accordingly, the stresses are moreevenly distributed over the rear face 28′.

Turning to FIGS. 6 and 7, the rear ferrule of the prior art arrangementof FIG. 1 is shown before and after make-up of the fitting. The fittingwas subjected to a finite element analysis, the results of which areparticularly evident in FIG. 7. There, shaded regions in the rear flangeof the rear ferrule and the nut evidence the force and stressconcentrations encountered upon make-up of the fitting. Particularly, aregion of high stress concentration is designated at area 60. Regions ofprogressively decreased stress concentration are identified by numerals62, 64, 66, 68, and 70. Thus, the large stress concentration at theradial inner location of the rear face 28′ results in increased torqueduring make-up and potential galling of the nut.

FIGS. 8 and 9 show another modified rear ferrule in accordance with theteachings of the present invention. This rear ferrule is the same asshown in FIG. 5. As particularly evident in FIG. 9, the region of highstress concentration is substantially reduced in size when compared toFIG. 7. This indicates that the stresses have been more uniformlydispersed over the rear face of the flange of the rear ferrule. Thus,the torque is reduced and the potential for galling is likewise reduced.

FIGS. 10 and 11 represent the rear ferrule shown and described in FIG.4. Here, the finite element analysis illustrates that the region of highstress concentration is substantially removed at the rear face and amore uniform distribution of stresses obtained. Again, the torque forcesassociated with make-up are thus reduced with the correspondingreduction in localized stress concentrations. The recess and conicalouter wall provide a radial component to the forces generated in thefitting and transferred through the rear ferrule while still providing adesired gripping and sealing of the tube.

The embodiment of FIGS. 12 and 13 also achieves these same objectives.The recess is of a slightly different configuration, i.e., the recess ismore sharply defined in the inner wall of the rear ferrule. It is alsoshifted slightly forwardly so that the deepest portion of the recess islocated forwardly of the rear flange. However, the outer wall is stillof conical configuration and in conjunction with the recess distributesthe stresses along the rear face of the rear ferrule.

As is apparent with the various embodiments described above, the recessand the tapered outer wall do not require a particular conformation toachieve the stress distribution and reduced torque for make-up of thefitting. In fact, a number of proposed alternative embodiments areillustrated in table form in FIG. 14. For example, the first row ofgeometries have a standard location that is generally defined as therear edge of the recess being located axially beneath the intersectionof the outer wall and the enlarged flange. The tear drop, righttriangle, rectangle, oval, square circular, obtuse triangle, curve, andcompound curve are various shapes that the recess may adopt. Moreover,the recess can be positioned at a forward location (second row), or arearward location where the deepest portion of the recess is positionedbeneath the enlarged flange (third row) while still adopting the variousconfigurations. Still further, the orientation of the shapes can bereversed as demonstrated by the various geometries in the fourth row orthe sixth row, or the recess may be defined by multiple recesses asshown in the geometries of the fifth and eighth rows. Alternatively, therecess(es) may be enlarged as indicated in the seventh and eighth rows.Accordingly, the invention is not limited to the particularconfigurations shown and described in the earlier embodiments of FIGS.2-13, but may also be incorporated into selected other geometricalconfigurations.

With reference to FIGS. 15-20, another embodiment of the invention isillustrated. As noted herein above, the use of a recess 40 in the rearferrule 22 significantly reduces stress concentrations at the drivesurface 32 of the drive nut 30 by adding a radial component to the pullup forces. The provision of the tapered outer wall 50 further cancontribute to the radial component and stress distribution, as well ascontrolled deformation of the rear ferrule 22 during pull up. Inaccordance with the embodiments of FIGS. 15-20, the rear ferrule isprovided with a contoured drive surface that further reduces stressconcentrations in the area of engagement between the drive nut 30 andthe rear ferrule 22.

FIG. 21 illustrates in an exemplary manner typical pull up stressdistributions at the dive nut drive surface 32 and the rear ferruledrive surface 28, typical in cases that incorporate a recess 40 typestructure in the rear ferrule as described herein before. These stressconcentrations are represented by the arrows 200. By comparing thestress distributions of FIG. 21 and the stress concentrations in FIG. 7(FIG. 7 being illustrative of a rear ferrule that does not include arecess-type or notch structure 40) it is apparent that the provision ofthe recess 40 concept significantly and substantially reduces stressconcentration on the drive nut drive surface 32 as noted hereinbefore.This reduction in stress concentrations is further evident from acomparison of FIG. 7 with FIGS. 9, 11 and 13.

Although FIG. 21 is not an FEA representation, it illustrates the pointthat the use of the recess 40 may not in all cases entirely eliminatestress concentrations at the rear surface of the rear ferrule (albeitthe use of the recess or notch 40 greatly reduces stress concentrationsin comparison to a rear ferrule that does not include a notch orrecess). In the simplified representation of FIG. 21, stressconcentrations may exist for example at the radially inner and outerportions of the rear ferrule flange 26 (referred to herein as bi-modalstress concentrations as they can occur though not have to occur as tworegions of stress concentrations). These somewhat higher bi-modal stressconcentrations are represented by the heavier arrows in FIG. 21. Thepresent invention is thus directed to further reducing such stressconcentrations, with the results illustrated in FIG. 19, wherein thearrows represent a substantial elimination of pull up forceconcentrations using a modified rear ferrule drive surface and therecessed inner radius.

In accordance with this further aspect of the invention a two ferrulefitting is shown having a rear ferrule which is modified so as to reducefurther the pull up stress concentrations by substantially distributingthe stress concentration along the rear surface that engages the drivesurface 32 of the drive nut 30. As is shown in FIGS. 15-18,corresponding fitting components are shown in finger-tight positionpreparatory to final tightening.

With specific reference to FIGS. 15 and 16, the fitting comprises a body110 having a cylindrical opening 112 for receiving a tube end 113 thatbottoms on a counterbore 112 a. A tapered, frusto-conical cam mouth 114is located at the axial rear or receiving end of the opening 112. Afront ferrule 116 having a smooth, cylindrical, radially inner wall 118is closely received on the tube 113. The front ferrule 116 has a taperedouter surface 120 which engages the tapered mouth 114 of the body 110.

Associated with the front ferrule 116 and located axially adjacent(i.e., in a rearward direction concentrically aligned with thelongitudinal axis of the fitting) is a rear ferrule 122 configured witha tapered nose portion 124 having a rearward, tapered surface 127. Therear ferrule 122 also includes a radially extending rear flange 126having a contoured end face 128. The contoured face 128 includes arearward-facing driven surface 129 which is engaged by a respectivedriving surface 132 of the drive nut 130.

The tapered nose surface 127 of the rear ferrule 122 engages and mayhave, but not necessarily, substantially the same angle as a tapered camsurface 125 in the rear area of the front ferrule 116. The nose portion124 is joined with the flange 126 by a preferably tapered outer wall131. In the illustrated embodiment the wall 131 tapers with anincreasing radial dimension in the axially rearward direction. The outerwall 131 could also be cylindrical, although it is preferred to betapered to further facilitate reduction of stress concentrations on therear surface 129.

The ferrules 116 and 122 are enclosed by a threaded drive nut member 130which includes a drive surface 132 that engages the contoured face 129of the rear ferrule 122. The nut member 130 threadably engages athreaded portion of the body 110. During tightening and make-up of thefitting, the drive surface 132 of the nut 130 applies pull up forcesagainst the contoured face 129 of the rear ferrule 122 to drive bothferrules axially forward (to the right as viewed in FIG. 16) into thefully engaged position shown in FIG. 19. The rear ferrule is configuredso that upon forced engagement with the tapered cam surface 125, thenose portion 124 deforms radially inward. This action is desirable sinceit results in a tight gripping engagement of the rear ferrule 122 innercylindrical wall with the outer surface of the wall of the tubing 113.

In the embodiments illustrated in FIGS. 15-20, the contoured face 128 ofthe rear ferrule 122 may be rounded, curved, arcuate, or bowed or othercurvilinear shape or combination of such shapes. Preferably but notnecessarily the face 128 has a portion of which is a contour in the formof a convex radius R. The center of the radius can be, for example,internal to the ferrule body as shown in FIG. 18. However, those skilledin the art will readily appreciate that the origin of the radius surface129 can be located anywhere with respect to the rear ferrule structurewith the illustration of FIG. 18 being provided for illustrativepurposes only. One aspect of the contoured face 128 is that with thedriven surface 129 in the form of a convex radius, a line contact 129 b(or reduced face to face radial contact) is formed initially with thenut drive surface 132, in a region between the inner and outer radialportions of the flange 126. The rear ferrule also preferably includes arecess 140 which can be of any configuration as previously describedherein above. Alternatively, the contoured rear face 128 can be usedwith a rear ferrule configuration that omits the recess 140, asillustrated in FIG. 20.

Although the use of a radius or other curvilinear surface for thecontoured surface 128 is desirable, there is a practical limit as to howsmall that radius can be made. If the radius of curvature is made toosmall then there will possibly be undesired stress concentrationsdevelop in the center region of the contoured face 128.

A distinct advantage of the contoured rear ferrule 122 is that pull upstresses between the nut drive surface 132 and the contoured face 128 ofthe rear ferrule 122 are more uniformly distributed across the surface128 of the rear ferrule, thus reducing and substantially eliminatingstress concentrations. This further reduction of stress concentrationson the drive nut 130 reduces pull up torque and reduces galling, thusfacilitating re-make of the fitting.

It is important to note that although the illustrated embodiments showan initial contact between the rear ferrule 122 and the drive nut 130 asgenerally in the middle of the contoured face 128, this is not requiredin every application. The initial point of contact will be a function ofthe overall fitting design, including the geometry of the tapered wall131, the recess 140, the nose portion 127, the front ferrule 116configuration and so forth. But in keeping with a general aspect of theinvention, the contoured face 128 will be convex or axially variant inthe region between the radial inner and outer portions of the flange 126so as to distribute more uniformly the pull up forces acting on thedrive nut 132 to reduce galling and pull up torque as compared to aconventional rear ferrule design that has a substantially flatnon-contoured driven surface 128.

FIG. 20 illustrates an embodiment of the invention in which the rearferrule 122′ has a substantially cylindrical inner wall 150′, butotherwise includes the flange 126′ having a contoured driven surface128′ and a nose portion 124′ with a front bevel 127 and a tapered outerwall 131′.

FIG. 22 illustrates another embodiment of the invention wherein the rearferrule 22′ design can have the recess 40′ shifted axially rearward,generally within the axial dimension of the flange 26′.

With reference to FIGS. 23A-F, we illustrate a number of variations ofthe contoured end face 128. In FIG. 23A the face 128 is formed with anelliptical profile. In FIG. 23B, the face 128 is formed by a blending ofmultiple radiuses such as sections 128 a, 128 b and 128 c (dots on thedrawing designate points of intersection of the arcs and not physicalfeatures of the end face). In FIG. 23C, the end face 128 includes acentral portion 128 a having a first radius profile, and outer portion128 b formed by a second radius profile. In FIG. 23D the end face 128includes a central portion 128 a having a profile formed by a radius andouter portions 128 b and 128 c formed as straight surfaces (in sectionthe surface appears straight, though realized in the form of a conicalsurface). In FIG. 23E the end face 128 includes an elliptical portion128 a and a straight portion 128 b. And in FIG. 23F the end face 128 hasa profile formed by three geometric shapes of an ellipse 128 a, astraight portion 128 b and a radius portion 128 c. In all the examplesof FIG. 23A-F the point made is that the selected profile and geometryfor the contoured end face 128, as with the earlier embodimentsdescribed hereinbefore, is designed to achieve the desired plasticdeformation of the rear ferrule 122 hinge-like nose to achieve excellentgripping of the tube while also maintaining the proper sequentialpull-up operation with the front ferrule.

With reference to FIGS. 24A-F, the present invention can also berealized by incorporating a contoured profile in the drive surface 132of the nut 130. In these embodiments, the rear driven surface 128 isconical. Alternatively, both the drive surface 132 and the drivensurface 128 could be contoured. FIGS. 24A-F correspond to FIGS. 23A-F asto the contour shape applied to the drive nut surface 132. Thus, FIG.24A illustrates an elliptical profile; FIG. 24B illustrates a multiplecircle profile; FIG. 24C illustrates a two radius surfaces; FIG. 24Dillustrates a radius surface and two straight portions; FIG. 24Eillustrates an ellipse contour with a straight portion; and FIG. 24Fillustrates a combination of a radius, straight and ellipse portions. Inyet another embodiment of FIG. 24G, the nut drive surface 132 can beformed of two straight portions that join at an apex 129D.

With reference to FIG. 25, in still a further embodiment, the rearferrule 522 include a recess 540 in the inner cylindrical wall. However,in this embodiment, the rear flat portion 542 is formed by a largerdiameter bore in the ferrule 522 body as compared to the diameter of thebore that forms the forward flat 544. By forming the rear surface 542with a larger diameter, a single tool can be used to form the notch 540and the central bores through the ferrule 522 body. The difference inthe two diameters is represented by the dimension D in FIG. 25. Notethat the notch or recess 540 is positioned in the rearward portion ofthe ferrule 522 body. This provides an axially elongated forward surface544 that assists in maintaining the ferrule in alignment during assemblysince the rear portion 542 does not as closely surround the tube. Thoseskilled in the art will readily appreciate, however, that the enlargeddiameter rear portion 542 can be used with many of the notch 40 profilesillustrated herein and others, including multiple notch designs. Therear ferrule 522 may also include a contoured rear wall as in theembodiments described herein.

FIG. 26 illustrates another embodiment of the rear ferrule 22′. In thisembodiment, in addition to the double notches 40′ in the central throughbore, the ferrule includes a notch or recess 300 in the outer diametersurface 50′ of the ferrule. This notch 300 can be used as part of the“hinge” design to further control the plastic deformation of the ferrulenose portion 52′ during pull-up. FIG. 27 illustrates a further exampleof a rear ferrule 622 that incorporates the central recess 640, atapered outer diameter 650 having an outer diameter recess or notch300′, and the larger diameter rear portion or radial flange 642 with acontoured or radius driven surface 628. The rear surface 642 is of aslightly larger diameter than the forward surface 644, as in otherexamples herein, as represented by the dimension D″. All of the actualdimensions and profiles may be selected to cause the ferrule 622 toplastically deform with desired loads against the tube surface andminimized load concentrations against the nut drive surface and alsoassure proper driving force into the front ferrule. As with the variousother rear ferrule designs illustrated herein, the various concepts ofthe rear ferrule design can be used in a single ferrule fitting.

The ferrule illustrated in FIG. 27 includes the outer notch 300′. TheFEA illustration of FIG. 28 dramatically shows how this outer notch 300′produces a significant hinge effect at the nose portion 652 of the rearferrule. The outer notch 300 is bounded by a radially extending crown302. This crown 302 functions to prevent the nose of the rear ferrule22′ from slipping (as, for example, in a telescoping manner) under thefront ferrule when the tubing is thin walled or otherwise easilydeformed during make-up of the fitting. Without the crown 302, as thethin tube wall collapsed the nose of the rear ferrule could be forcedout of the camming mouth of the front ferrule and slip under the frontferrule, preventing proper sequential pull-up and poor gripping byeither ferrule. Preferably, the crown 302 maintains contact with theinner camming mouth of the front ferrule during pull-up.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

Having thus described the invention, it is claimed:
 1. A tube fittingcomprising: a fitting body having a cylindrical bore for receiving atube end and including a tapered mouth at one end of said bore; a drivemember having a threaded engagement with said body and having a ferruledrive surface; a first ferrule having a tapered first end that extendsinto said tapered mouth of the fitting body and having a second end witha tapered recess forming a camming surface that axially extends towardsaid first end; and a second ferrule having a generally cylindricalinterior wall, a tapered first end that extends into said tapered recessand engages said camming surface of said first ferrule, a tapered outerwall portion, and a driven surface on a second end thereof that engagessaid drive member ferrule drive surface; said second ferrule interiorwall having a first circumferential recess located between said firstand second ends of said second ferrule; said tapered wall portion havinga second circumferential recess near said first end; wherein said secondferrule driven surface comprises a contoured face and that with saidfirst and second circumferential recesses produce a radial component inpull up forces occurring at said drive surface to distribute moreuniformly said pull up forces across an interface area between saiddrive surface and said contoured face as compared to force concentrationareas that would otherwise be present at said interface area in absenceof said contoured face and said first and second circumferential recess.2. The fitting of claim 1 wherein said drive member axially drives saidsecond ferrule into said first ferrule tapered recess and axially drivessaid first ferrule into said body tapered mouth when said drive memberis pulled up with said body.
 3. The fitting of claim 1 wherein saidsecond ferrule second circumferential recess has an increasing radialdepth in the axial direction toward said second ferrule second end. 4.The fitting of claim 1 wherein said second ferrule tapered outer wallincludes a radially extending crown adjacent said first end.
 5. Thefitting of claim 4 wherein said crown remains in contact with said firstferrule tapered recess during pull-up of the fitting.
 6. The ferrule ofclaim 1 wherein said second ferrule is case hardened over a portion ofits surface.
 7. The ferrule of claim 1 wherein said second ferrule iscase hardened over its entire surface.
 8. A tube fitting comprising: afitting body having a cylindrical bore for receiving a tube end andincluding a tapered mouth at one end of said bore; a drive member havinga threaded engagement with said body and having a ferrule drive surface;a first ferrule having a tapered first end that extends into saidtapered mouth of the fitting body and having a second end with a taperedrecess that axially extends toward said first end; and a second ferrulehaving a generally cylindrical interior wall, a tapered first end thatextends into said tapered recess of said first ferrule, and a drivensurface on a second end thereof that engages said drive member ferruledrive surface; said second ferrule interior wall having a firstcircumferential recess located between said first and second ends ofsaid second ferrule; said nut drive surface being contoured; saidcontoured drive surface and said recess reducing force concentrations onsaid drive member drive surface when the fitting is pulled up; whereinsaid drive surface comprises a radius portion.
 9. A tube fittingcomprising: a fitting body having a cylindrical bore for receiving atube end and including a tapered mouth at one end of said bore; a drivemember having a threaded engagement with said body and having a ferruledrive surface; a first ferrule having a tapered first end that extendsinto said tapered mouth of the fitting body and having a second end witha tapered recess that axially extends toward said first end; and asecond ferrule having a generally cylindrical interior wall, a taperedfirst end that extends into said tapered recess of said first ferrule,and a driven surface on a second end thereof that engages said drivemember ferrule drive surface; said second ferrule interior wall having afirst circumferential recess located between said first and second endsof said second ferrule; said nut drive surface being contoured; saidcontoured drive surface and said recess reducing force concentrations onsaid drive member drive surface when the fitting is pulled up; whereinsaid drive surface comprises a curvilinear portion.
 10. A tube fittingcomprising: a fitting body having a cylindrical bore for receiving atube end and including a tapered mouth at one end of said bore; a drivemember having a threaded engagement with said body and having a ferruledrive surface; a first ferrule having a tapered first end that extendsinto said tapered mouth of the fitting body and having a second end witha tapered recess that axially extends toward said first end; and asecond ferrule having a generally cylindrical interior wall, a taperedfirst end that extends into said tapered recess of said first ferrule,and a driven surface on a second end thereof that engages said drivemember ferrule drive surface; said second ferrule interior wall having afirst circumferential recess located between said first and second endsof said second ferrule; said nut drive surface being contoured; saidcontoured drive surface and said recess reducing force concentrations onsaid drive member drive surface when the fitting is pulled up; whereinsaid drive surface comprises at least two non-parallel straightportions.